Van der Waals Epitaxial Growth of Atomic Layered HfS Crystals for Ultrasensitive Near-Infrared Phototransistors.

As a member of the group IVB transition metal dichalcogenides (TMDs) family, hafnium disulfide (HfS ) is recently predicted to exhibit higher carrier mobility and higher tunneling current density than group VIB (Mo and W) TMDs. However, the synthesis of high-quality HfS crystals, sparsely reported, has greatly hindered the development of this new field. Here, a facile strategy for controlled synthesis of high-quality atomic layered HfS crystals by van der Waals epitaxy is reported. Density functional theory calculations are applied to elucidate the systematic epitaxial growth process of the S-edge and Hf-edge. Impressively, the HfS back-gate field-effect transistors display a competitive mobility of 7.6 cm V s and an ultrahigh on/off ratio exceeding 10 . Meanwhile, ultrasensitive near-infrared phototransistors based on the HfS crystals (indirect bandgap ≈1.45 eV) exhibit an ultrahigh responsivity exceeding 3.08 × 10 A W , which is 10 -fold higher than 9 × 10 A W obtained from the multilayer MoS in near-infrared photodetection. Moreover, an ultrahigh photogain exceeding 4.72 × 10 and an ultrahigh detectivity exceeding 4.01 × 10 Jones, superior to the vast majority of the reported 2D-materials-based phototransistors, imply a great promise in TMD-based 2D electronic and optoelectronic applications.